Method of making header joint for a clad tubulation

ABSTRACT

A ferrous core-forming tube is internally and externally clad with titanium. The ferrous core is chemically etched away from between the claddings for some distance from their ends so that these ends extend from the core. The tube thus prepared is inserted through an opening in a header with said ends adjacent one side of the header. These ends are then flared outwardly into engagement with the adjacent side of the header and sealingly welded thereto. In cases in which the cladding is not strong and/or is thin a cylindrical slug or thimble of titanium is inserted into the etched-out space prior to flaring and welding.

United States Patent [72] Inventor Sheldon S. White Brookline, Mass. [21] Appl. No. 770,172 {22] Filed Oct. 24,1968 [45] Patented Dec. 21,1971 [73] Assignee Texas Instruments Incorporated Dallas, Tex.

[54] METHOD OF MAKING HEADER JOINT FOR A CLAD TUBULATION 6 Claims, 8 Drawing Figs.

[52] US. Cl 29/157.4, 29/472.1, 29/475, 29/511 [51] Int. Cl ..B2ld 53/00, B2lk 29/00, 823p 15/26 [50] Field of Search 29/482, 478, 479,157.4, 157.3, 422, 511, 423, 473.3, 481, 475, 472.1

[56] References Cited UNITED STATES PATENTS 2,024,782 12/1935 Schwinn 29/478 X 2,368,403 1/1945 Barnes 29/482 X 3,207,215 9/1965 Whittell, Jr 29/157.4 UX

3,479,730 11/1969 Poth 29/482 X 356,234 1/1887 Shader 29/481 1,981,915 11/1934 Hormel et a1. 29/423 UX OTHER REFERENCES The O. G. Defensive Publication Tor, Def. Pub. of Serial No. 698,485 filed 12/11/67, published in 860 O. G. 1008. on 3/25/69.

Primary Examiner-John F. Campbell Assistant Examiner- Ronald J. Shore Attorneys-Harold Levine, Edward .1. Connors, Jr., John A.

Haug and James P. McAndrews thimble of titanium is inserted into the etched-out space priorto flaring and welding.

PATENIEDHECZI an 3528.923

SHEET 1 [1F 2 FIGW 4 MTENTEU UEEZ'I WI SHEET 2 BF 2 FIG.

FIG.5

FIG.7

METHOD OF MAKING HEADER JOINT FOR A CLAD TUBULA'IION Clad tubing in general has as its purpose usefulness in corrosive environments. However, in the fabrication of welded joints between clad tubing and headers, problems often arise due to incompatibility between the tubing core material and the header material. For example, in the case of titanium-clad, low-carbon steel tubing, fusion welding to a titanium header may lead to the formation of undesirable interrnetallic compounds in the presence of fluid (liquid or gas) such as will produce a galvanic effect. Or, the core and cladding materials may be metallurgically incompatible in noncorrosive environments to the extent that embrittling intermetallic compounds will be formed simply upon welding. I overcome these difficulties by sealing off the clad core from exposure to ambient gases or fluids and from taking part in the weldment.

Referring to the drawings;

FIG. 1 is an axial section of an end portion of a low-carbon tubular core, internally and externally clad with titanium;

FIG. 2 is a view similar to FIG. 1 after performance of an etching operation on the core;

FIG. 3 is a view similar to FIG. 2 illustrating a flaring operation;

FIG. 4 is a view similar to FIG. 3 illustrating a welding operation; and

FIGS. 5-8 are views similar to FIGS. 1-4 respectively, illustrating another form of the invention.

Corresponding reference characters indicate similar parts throughout the drawings. The drawings are illustrative and not to scale.

Referring more particularly to FIG. 1, there is shown at numeral 1 one end of a length of low-carbon steel tubing forming a tubular core which has interior cladding 3 and exterior cladding 5, both composed of titanium which, unlike the core, is substantially noncorrodible.

As illustrated in FIG. 2 the steel tubing 1 is acid-etched for a distance D from between the ends of the cladding 3 and 5. For this purpose may be used any of the well-known iron-etching acid materials which do not attack titanium, such as nitric acid or commercial grade sulfuric acid.

Next, as shown in FIG. 3, the etched end of the tube is flared by a conventional flaring tool. This may occur before or after the clad tube is inserted in an opening 7 in a header 9 (FIG. 4). In either event, the bent'end of the inner cladding 3 engages the bent end of the outer cladding 5 so as to enclose the end of the steel tubing 1. The flared ends are pushed into engagement with header 9 around opening 7 and then welded thereto and to one another as indicated at 13. Thus the desired connection is made between the clad tubing and the header without the ferrous material of the tubing l entering into the all-titanium weldment l3 and so as to prevent access to the core 1 of any corrosive ambient fluids.

In some cases the cladding layers, either because of the manner in which they are applied to the tubular core (as for example by electroplating), or because of their thinness, are not strong and/or incapable of being properly flared or welded. Such a condition may be assumed in the illustrations of FIGS. 5-8, in which numeral 1 again represents a length of low-carbon steel tubing as in FIG. 1. But in this case it is assumed that the inner and outer claddings l5 and 17 have been electroplated or otherwise applied thinly or not so strongly, so that after etching to the depth D as illustrated in FIG. 6, the projecting portions of the cladding are incapable in their unsupported condition of being properly joined. Therefore as illustrated in FIG. 7, an annulus, thimble or sleeve of titanium is inserted between the ends of the cladding within the annular space of depth D. This cylindrical sleeve is only slightly smaller in all of its physical dimensions than those of the space from which the low-carbon steel tubing has been removed by etching. Thus, the exposed ends of the cladding become supported by the titanium sleeve I9 so that the flaring and welding operations may be properly accomplished (FIG. 8). In the flaring operation the sleeve also is flared and enters into the weldment as illustrated at 13. In this case, as in the one illustrated in FIG. 1-4, no ferrous material is exposed to ambient corrosive atmospheres or fluids, nor does it enter into the weldment 13.

While the invention has been described for the case of titanium-clad ferrous tubing for attachment to a titanium header, it will be understood that it is applicable to any combination of metals for these parts in connection with which the problems arise, as above set forth.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

I. A method for protecting the core of a composite metal tubulation at one end of the tubulation where the tubulation is composed of a first material having inner and outer claddings of a second material which is incompatible with said first material during fusion welding thereof, said method comprising the steps of removing said core material from between said claddings for a selected distance away from said end of said tubulation to leave ends of said inner and outer claddings extending from said core tube, inserting a cylindrical metal sleeve of said second material between said extending cladding ends and welding said extending cladding ends to said sleeve.

2. A method for fabricating ajoint between a header and a tubulation composed of a metal core tube of a first material having inner and outer metal claddings of a second material which is incompatible with said first material during fusion welding thereof comprising the steps of removing said core material from between said claddings for a selected distance away from one end of said tubulation to leave ends of said inner and outer claddings extending from said core tube, inserting a cylindrical metal sleeve of said second material between said extending cladding ends and joining said extending cladding ends each to said sleeve and to said header around an opening in said header by welding.

3. A method for fabricating a joint between a titanium metal header and a tubulation composed of a steel core tube having inner and outer titanium claddings, said method comprising the steps of etching away said core material for a selected distance from one end of said tubulation by use of an etchant which does not attach said cladding materials to leave ends of said claddings extending from said core tube, flaring said extending cladding ends, and joining said extending cladding ends together and to said header around an opening in said header by welding.

4. A method as set forth in claim 3 wherein said extending cladding ends are flared into engagement with each other and wherein said cladding ends are welded directly to each other and to said header.

5. A method as set forth in claim 3 wherein a cylindrical titanium sleeve is inserted between said extending cladding ends prior to flaring thereof, wherein said sleeve and extending cladding ends are flared together, and wherein said extending cladding ends are welded to said sleeve and to said header around said header opening.

6. A method for fabricating a joint between a metal header and a tubulation composed of an inner metal core tube of a first material having inner and outer metal claddings of a second material which is incompatible with said first material during fusion welding thereof comprising the steps of etching said core material with an etchant which does not attach said cladding materials to remove said core material from between said claddings for a selected distance away from one end of said tubulation to leave ends of said inner and outer claddings extending from said core tube, inserting a cylindrical metal sleeve of said second material between the extending cladding ends, flaring said extending cladding ends and said insert, and

joining said extending cladding ends together and to said header around an opening in said header by welding. 

2. A method for fabricating a joint between a header and a tubulation composed of a metal core tube of a first material having inner and outer metal claddings of a second material which is incompatible with said first material during fusion welding thereof comprising the steps of removing said core material from between said claddings for a selected distance away from one end of said tubulation to leave ends of said inner and outer claddings extending from said core tube, inserting a cylindrical metal sleeve of said second material between said extending cladding ends and joining said extending cladding ends each to said sleeve and to said header around an opening in said header by welding.
 3. A method for fabricating a joint between A titanium metal header and a tubulation composed of a steel core tube having inner and outer titanium claddings, said method comprising the steps of etching away said core material for a selected distance from one end of said tubulation by use of an etchant which does not attach said cladding materials to leave ends of said claddings extending from said core tube, flaring said extending cladding ends, and joining said extending cladding ends together and to said header around an opening in said header by welding.
 4. A method as set forth in claim 3 wherein said extending cladding ends are flared into engagement with each other and wherein said cladding ends are welded directly to each other and to said header.
 5. A method as set forth in claim 3 wherein a cylindrical titanium sleeve is inserted between said extending cladding ends prior to flaring thereof, wherein said sleeve and extending cladding ends are flared together, and wherein said extending cladding ends are welded to said sleeve and to said header around said header opening.
 6. A method for fabricating a joint between a metal header and a tubulation composed of an inner metal core tube of a first material having inner and outer metal claddings of a second material which is incompatible with said first material during fusion welding thereof comprising the steps of etching said core material with an etchant which does not attach said cladding materials to remove said core material from between said claddings for a selected distance away from one end of said tubulation to leave ends of said inner and outer claddings extending from said core tube, inserting a cylindrical metal sleeve of said second material between the extending cladding ends, flaring said extending cladding ends and said insert, and joining said extending cladding ends together and to said header around an opening in said header by welding. 